Tokkai Hei 3-67042 published by the Japanese Patent Office in 1991 and Tokkai Hei 8-144803 published by the Japanese Patent Office in 1996 indicate a "traction controller" in which a slip of vehicle drive wheels is suppressed by lowering the vehicle wheel drive force.
The slip of drive wheels may occur due to the state of a road surface during vehicle acceleration, and this device suppresses the slip by reducing the output torque of the engine according to a wheel slip factor.
Reduction of the output torque is performed for example by cutting fuel supply to some of the cylinders of the engine.
When an engine which performs stratified combustion is combined with such a drive force controller, however, the following problem arises. Stratified combustion refers to combustion where fuel is injected directly into the cylinder in the latter half of a compression stroke of a piston in the cylinder, and a combustible air-fuel mixture layer is formed around the spark plug. In this type of combustion, stable combustion can be performed while keeping the air-fuel ratio extremely lean in the whole combustion chamber. The stratified combustion is generally performed in the low load region of the engine where high engine output is not required. In the high load region where high engine output is required, fuel injection is performed in the intake stroke, and uniform combustion of a homogeneous air-fuel mixture is performed in the vicinity of the stoichiometric air-fuel ratio.
Therefore it is in the running region where the required engine output torque is comparatively small that the engine performs stratified combustion.
Even in this case, when road surface friction is low, e.g. when the road surface freezes, the traction controller cuts the fuel supply to a specific cylinder or cylinders. Slip is thereby suppressed, and fuel supply to all cylinders is resumed again when ordinary running conditions have returned.
However, if the temperature of the combustion chamber falls due to cutting of the fuel supply, there is a risk that stratified combustion will not become stable just after the recovery of fuel supply and misfiring may occur in the combustion chamber.
Even when drive force reduction control is performed by retarding the ignition timing, reducing the throttle opening or reducing the supercharging pressure in a supercharging engine, stratified combustion may also not become stable when it is performed immediately after the termination of the drive force reduction control.